# Calibrating a knapsack sprayer with the current NSTS sheet

URL: https://leafwrit.com/uk/knapsack-calibration-sheet/
Reviewed: 2026-10-29

**Calibrating a knapsack sprayer means measuring water delivered over a known area at the operator's working pace.** Open the [NSTS Liquid equipment page](https://www.nsts.org.uk/Tests/Liquid) and follow its handheld checklist link. The **V6.07.2025** document contains inspection checks followed by a **Sprayer Calibration Sheet**. Use clean water for measurements and the actual pesticide label for the eventual chemical dose.

## Identify the machine and finish the condition checks

The first section identifies the company or owner, address, operator and certificate number, sprayer make and model, serial number, inspector and inspection date.

Inspect a clean, empty, depressurised sprayer under the manufacturer's instructions. Check the lid seal and vent, tank strainer, tank, straps, hoses, trigger, lance, filters, nozzle and pump. For an electric machine, include the battery and charger. The sheet has pass, fail and repair-action columns; a calibration result cannot resolve a leak recorded in that inspection.

Complete the clean-water function checks before the calibration walk. These include tank graduations, loaded stability, pump operation, pressure relief where fitted, valve operation, leaks during and after spraying, and an even nozzle pattern. Wear the suitable protective equipment identified for the inspection.

## Enter the label requirements before changing the setup

Record the required application volume, chemical dose and spray quality in the first calibration action. Select the nozzle and equipment, then set pressure where it can be adjusted. Use the nozzle manufacturer's chart to relate pressure, output and spray quality.

Keep water volume and chemical dose in separate columns. Litres of spray mixture per hectare describe carrier delivery; litres or kilograms of product per hectare describe the pesticide quantity. Some labels express concentration per volume of water and also impose an area-based maximum. Both conditions apply.

## Electric knapsack sprayer: check the battery and charger first

**Before calibrating an electric knapsack sprayer, check the condition of the battery and the charger, with extra care for lithium-ion batteries.** Do this in the inspection before the calibration walk, and do not proceed if you find chemical residue, damage or leakage. Calibrate with a charged battery and note on the sheet the pump setting used, because the measured output belongs to that setting.

## Measure working width and the timed walking strip

Hold the trigger and lance at a comfortable working height over the target. With clean water, spray a dry surface and measure the resulting band in metres. This is the working spray width for the calculation.

Walk and spray a **100 metre strip** under conditions representative of the job, wearing the intended equipment and carrying a full sprayer. Repeat the walk and average the times. Keep the same nozzle, pressure setting and working technique for the collection measurement. The operator's pace is part of the calibration.

Spray into a measuring vessel for the average time taken over the strip. Maintain steady pumping, repeat the collection and average the quantities.

## Calculate delivery and prepare a part-tank load

For the NSTS strip method, walking speed in kilometres per hour is **360 divided by the seconds taken over 100 metres**. Applied volume in litres per hectare is **collected litres multiplied by 100, divided by spray width in metres**. The collected volume in the second formula is the amount discharged during that same strip time.

**Invented calculation example:** a measured band is **1.2 m** wide; the average time over **100 m** is **80 seconds**; average output collected during **80 seconds** is **2.4 litres**. These are illustrative measurements, not a recommended setup or pesticide dose.

| Calculation | Working | Result |
| --- | --- | --- |
| Walking speed | 360 ÷ 80 | 4.5 km/h |
| Strip area | 100 × 1.2 | 120 m² |
| Spray volume | 2.4 × 100 ÷ 1.2 | 200 L/ha |
| Area of the example bed | 30 × 4 | 120 m² |
| Mixture required for that bed | 200 × 120 ÷ 10,000 | 2.4 L |

**Continue the invented example:** assume, only for this calculation, that the actual permitted product dose were **3 L/ha**. The example bed would require **3 × 120 ÷ 10,000 = 0.036 L**, or **36 ml** of product. A **10 litre final spray-mixture fill** at the measured **200 L/ha** would cover **0.05 ha** and contain **150 ml** at that hypothetical dose. The chemical is included within the final mixture volume.

The real dose comes in the units printed on the label; a rate in grams stays in mass. For a part fill, the area covered is that of the final fill, not of the backpack's nominal capacity. The [tank calculation guide](/uk/spray-tank-mix-calculator/) continues the arithmetic.

## Adjust and remeasure the working setup

If delivery misses the required application range, change nozzle, spray width or pace as appropriate, then repeat the measurement. Raising pressure can also alter spray quality, so check the nozzle chart whenever that setting changes.

A pressure gauge that does not return to zero needs attention before it is used as a reference. With a long hose, pressure at the pump and at the application device can differ.

## Keep the measurement with the application record

Keep a spray record with all the data above: nozzle type, pressure, width, times and measured output.

Calibration establishes delivery; the label supplies the crop or situation, application limits and protection conditions. During filling, remain with the sprayer and prevent overflow. The [knapsack selection guide](/uk/knapsack-sprayer-selection/) covers choice and servicing.

## Finish the storage checks without damaging the nozzle

Prepare the sprayer for storage separately from inspection and function testing. Empty and depressurise as directed for that model, clean and dry the outside including straps, and clean tips and filters with a soft brush. Sharp objects can damage a nozzle orifice. Use the specified lubricant for moving seals such as plunger cups or O rings. Store the clean machine securely, protected from frost and direct sunlight.

Residues can remain in the tank, hose, trigger filter and tip. Prevent contaminated rinsings reaching drains or watercourses.

## Nozzle types on a knapsack lance

Hydraulic nozzles used on knapsack lances include hollow-cone, flat-fan and anvil or flood-jet patterns. Their distribution differs. For ornamental-crop application, cone patterns suit insecticide and fungicide coverage; fan or anvil patterns suit herbicide application.

An adjustable pistol can deliver different output after its swivel grip is moved and reset. Small wrist movements can change overlap and deposition.

## Keep the worksheet units consistent

Use a stopwatch for elapsed seconds, a measured strip for distance and a graduated collecting vessel for volume. The function-check section includes the visibility and accuracy of the tank graduations.

In the invented example above, the measured discharge is **2.4 litres per 80 seconds**, equivalent to **1.8 litres per minute**. Substituting **1.8** into the strip formula as though it were the 80-second collection would produce **150 L/ha**, an incorrect result. The missing factor is the ratio between the two collection durations.

## Next step

Choose a machine with the [knapsack selection guide](/uk/knapsack-sprayer-selection/), check output in the [nozzle chart](/uk/sprayer-nozzle-chart/) and scale a load with the [tank calculator](/uk/spray-tank-mix-calculator/).

### Where is the knapsack sprayer calibration sheet?

The current NSTS handheld checklist links from its Liquid tests page. Version V6.07.2025 includes a Sprayer Calibration Sheet after the inspection sections.

### How do I measure output when calibrating a knapsack sprayer?

With clean water, measure spray width and average the timed 100 metre walk. Collect output for that same duration, repeating the measurement.

### Does a new nozzle remove the need to calibrate?

No. Applied volume also depends on pressure, working width and the operator’s pace. Measure the installed setup.

### Can I copy the dose printed in the NSTS example?

No. It is an example. Enter the dose and application requirements from the actual product label, then calculate the quantity for the measured area or fill.